Polyketone polymers are semi-crystalline polymers which possess an attractive set of properties for a variety of applications. The utility of these polymers can be further broadened by selectively blending polyketone polymers with other materials which have complimentary property sets.
The mixing together of two or more polymers has attracted interest as a means of arriving at new property combinations without the need to synthesize novel structures. The most common polymer blends are immiscible. In most cases, when two polymers are mixed, the components tend to segregate into separate phases, forming a non-adhering, heterogeneous mixture that exhibits inferior overall properties.
However, on rare occasions, polymer pairs will form miscible blends. The term miscible describes a mixture of two or more polymers that form a single-phase solution (solid or liquid) within the amorphous phase on a molecular scale. When one or both of the polymer blend components is capable of forming both a crystalline and an amorphous phase (i.e. a semicrystalline polymer), then the term miscible refers only to the amorphous phase in which the separate components are capable of mixing on the molecular level. Miscibility is indicated by a single glass transition temperature for a blend of two or more components.
Blends which exhibit isomorphism are even more rare than miscible blends. The term isomorphic will be used herein to describe a mixture of two or more polymers that co-crystallize, exhibiting only one crystallization point temperature (and also, only one melting point temperature). Isomorphic polymer pairs form both a miscible blend in the melt and cocrystallize when converted to the solid state.
Examples of isomorphic polymer pairs include aromatic polyetherketone polymer pairs and binary blends of copolymers of vinylidene fluoride and trifluoroethylene. U.S. Pat. No. 4,609,714 (Harris et al.), incorporated herein by reference, discloses isomorphic poly(aryl ether) resin pairs and also provides a description of isomorphism. Isomorphic polymer systems require the different types of monomer units to have approximately the same shape and volume (to allow co-crystallization), and to have a chemical attraction that promotes miscibility in the melt phase.
It is an object of this invention to provide an isomorphic blend of two or more polyketone polymers.